Processing line for the continuous processing of metal strips having a dual purpose of producing strips that are annealed and dip-coated or not coated, and corresponding cooling tower and method for switching from one configuration to the other

ABSTRACT

Disclosed is a treatment line for the continuous treatment of metal strips having a dual purpose, i.e. for producing strips that are annealed and dip-coated with a metal alloy and for producing strips that are annealed and not coated, comprising a dual-purpose cooling tower, i.e. for cooling strips that are annealed and not coated in a non-oxidizing atmosphere and for air-cooling strips that are annealed and coated.

TECHNICAL FIELD OF THE INVENTION

The invention relates to the field of production lines for coils of metal strips having a dual purpose of producing either strips that are annealed and dip-coated or strips that are annealed only, that is to say, uncoated. The coating can be of any type, based on zinc, aluminum, a mixture of zinc and aluminum, or any other component. More specifically, the invention relates to devices and methods that make it possible to give a line a dual purpose, with an operation in annealing-only mode or in annealing, then coating mode, with easy switching from one operating mode to the other.

Technical Problems Addressed by the Invention

The market needs for high-strength steel coils are such that steelmakers are looking for flexible means of production, allowing the production of steels that are annealed only and steels that are both annealed and coated. In addition, the new steels do not require the same thermal cycles when they are annealed only and when they are annealed and coated; this results in a line configuration with heating and cooling means that must be suitable for a wide variety of thermal cycles, which is difficult to achieve in a single line.

For example, for certain types of steel, it is customary, after a rapid cooling section, to keep the strip at temperature for a certain time before finalizing the heat treatment of the strip, and therefore to take it out of the treatment furnace. In annealing mode, the steel strip is generally cooled to a temperature below 200° C., typically of approximately 150° C., in a cooling section, before it leaves the furnace, in order to avoid the problems of oxidation of the strip in the open air that would result from leaving the strip at too high a temperature. In the present description, for this mode, the final cooling section refers to the cooling section that has just been described.

In the coated mode, it is necessary to bring the strip to a temperature close to that of the coating bath before it is immersed therein. This temperature varies according to the type of coating produced. It is for example 460° C. for galvanizing, but it is always much higher than the temperature of 150° C. targeted at the end of cooling in annealing mode. On leaving the coating bath, the strip is in the open air. It can then undergo a heat treatment modifying the quality of the coating (galvannealing) before a step of air cooling followed by water cooling to bring it to a temperature close to ambient temperature. In the present description, for this mode, the final cooling section refers to the last cooling section upstream of the coating bath, in the direction of travel of the strip.

The design of the final cooling section of an annealing line does not make it possible to prolong the maintenance of the strip at temperature before starting the cooling. Thus, the start of cooling of the strip necessarily begins as soon as the latter enters the final cooling section. The cooling rate of the strip is imposed by the concerned metallurgical structure. Thus, it is not possible to reduce the cooling capacity so that the cooling of the strip is distributed along the final cooling section. As a result, the cooling of the strip can be completed long before the end of the final cooling section.

When in coating mode, it may then be necessary to keep the end of the final cooling section at a sufficient temperature before the strip enters the coating bath, for example at 460° C. Indeed, if the strip is too cold when it arrives in the coating bath, the bath will cool (since the power that can be installed on a coating tank is limited) and will therefore generate mattes that will cause problems with the coating quality or with the management of the temperature of the bath. In addition, by being kept at temperature, the final cooling section increases the hold time. The final cooling section must therefore comprise heating means allowing this.

It therefore becomes obvious that the final cooling section, which is useful in annealing mode, generates additional stresses in coated mode.

The present invention provides a solution to the problem of using the same equipment, the final cooling section when it is present, in annealing mode and in coated mode. The present invention also minimizes problems caused by the presence of said final cooling section, which is always necessary in annealing mode, but which is not necessary in certain configurations in coated mode.

To facilitate the description of the invention, reference will be made to CAL mode to denote an operation of the line in annealing mode only, without metallic coating during quenching, and to CGL mode to denote an operation of the line in annealing and coating mode during quenching, independent of the nature of the coating. CAL is the acronym commonly used to denote an annealing line (for “Continuous Annealing Line”), and CGL is the acronym used to designate a galvanizing line (for “Continuous Galvanizing Line”).

TECHNICAL BACKGROUND

Document JP2004346359 is known, which discloses a cooling tower used in a non-oxidizing atmosphere. The document does not disclose a cooling section designed to operate with both line configurations, that is to say, also in air.

Document EP0072874 is known, which describes an installation with a dual configuration for manufacturing cold-rolled steel sheets and hot-coated galvanized steel sheets, which comprises, arranged successively in series, a heating zone, an equalization zone, a primary cooling zone, an overaging zone, with the possibility of controlled cooling, hot-dip galvanizing means, intermediate cooling means, a secondary cooling zone, hardening rolling means, and chemical treatment means. In the uncoated annealed strip production configuration, the strip does not pass through the cooling tower, which is circumvented by means of a bypass to directly connect the overaging zone and the secondary cooling zone.

EP3181709 describes a solution allowing the switch from a CGL mode to a CAL mode and vice versa. It mainly consists in having devices placed at the exit from the furnace, upstream of the coating bath, to ensure the sealing of the furnace in CAL mode, when the bath is removed and the bottom roll of the bath is replaced, instead, by a deflector roll. This solution does not address the technical problems mentioned above, since the final cooling section of the furnace must be dimensioned to allow cooling of the strip to approximately 150° C. in CAL mode.

EP1325163 describes a combined steel treatment line with a bypass installation for the coating zone and the cooling tower allowing the switch from a CGL mode to a CAL mode and vice versa. The bypass installation makes it possible to transfer the strip from the annealing furnace to the water tank placed at the outlet of the cooling tower without it being exposed to the ambient air. The bypass installation is placed above the galvanizing pot and the bath area equipment. This solution is not fully satisfactory, in particular because it complicates the arrangement of the line and it does not make it possible to benefit from the air cooling means of the cooling tower in annealing mode.

In addition, these solutions do not adequately meet the needs of steelmakers because, for a target steel quality, it may be difficult to achieve all of the desired thermal cycles in CAL and CGL modes due to the routing constraints of the strip in successive sections and the cooling means available therein.

The invention makes it possible to address these technical problems with a dual-use CAL/CGL line that does not significantly modify the thermal cycle of the steel grade targeted in CAL mode and in CGL mode, while allowing optimized use of the cooling equipment. These two aspects are obtained by allowing the cooling equipment installed in the cooling tower to operate in different modes, oxidizing or reducing for the strip depending on the coolant used, allowing the capacity of the final cooling section in the furnace to be reduced, or even allowing it to be eliminated.

DISCLOSURE OF THE INVENTION

To this end, there is provided, according to a first aspect of the invention, a cooling tower for a continuous treatment line for metal strips having a dual purpose, which has a configuration for producing strips that are annealed and dip-coated and a configuration for producing strips that are annealed and not coated.

The tower according to the first aspect of the invention is designed to operate in both line configurations. It comprises blowing means for cooling the strip selectively under a non-oxidizing atmosphere in the configuration for uncoated annealed strips and under air in the configuration for annealed and coated strips.

According to the invention, in the configuration for producing uncoated annealed strips, the strip passes through the cooling tower. Thus, the same cooling tower is used in each of the configurations. It is thus possible to pool the cooling means of the cooling tower.

Advantageously, the tower according to the first aspect of the invention can further comprise cooling sections connected together to form a sealed cooling tunnel. The sealed cooling tunnel may further be formed by connecting tunnels interposed between two cooling sections and/or other elements. The sealed tunnel can extend only on the rising strand, or on the rising strand and on the descending strand.

According to one embodiment, the tower according to the first aspect of the invention may further comprise, in the direction of travel of the strip, in the configuration for producing uncoated annealed strips, means for sampling a non-oxidizing atmosphere present at the strip upstream of the blowing means, means for recirculating and cooling said sampled atmosphere, the blowing means being arranged to blow the sampled, cooled and recirculated atmosphere.

According to a second aspect of the invention, there is provided a method for switching from one configuration to another of a cooling tower according to the first aspect of the invention, or one or more of its improvements, comprising the following steps:

-   -   for switching to the configuration for producing strips that are         annealed and not dip-coated with a metal alloy, connecting the         blowing means to a non-oxidizing atmosphere,     -   for switching to the configuration for producing annealed and         coated strips: connecting the blowing means to air.

According to a third aspect of the invention, there is proposed a continuous treatment line for metal strips having a dual purpose, which has a configuration for producing strips that are annealed and dip-coated and a configuration for producing strips that are annealed and not coated.

The continuous treatment line according to the third aspect of the invention comprises a cooling tower according to the first aspect of the invention, or with one or more of its improvements.

Preferably, the line comprises, successively in the direction of travel of the strip, an immersion tunnel, a bath area provided with equipment in said configuration for producing strips that are annealed and dip-coated in a metal alloy, and a cooling tower having a rising strand and a descending strand.

Preferably, the bath area is removable and can be replaced by a box designed to provide a sealed fluid connection between the immersion tunnel and the cooling tower.

According to one possibility, the cooling line according to the third aspect of the invention does not have a final cooling section.

According to a fourth aspect of the invention, there is provided a method for switching from one configuration to another of a treatment line for the continuous treatment of metal strips having a dual, according to the third aspect of the invention, or to one or more of its improvements, comprising the steps of the method for switching from said configuration to said other configuration of a cooling tower according to the second aspect of the invention, or one or more of its improvements, and further comprising the following steps:

-   -   to switch to the configuration for producing annealed strips not         dip-coated in a metal alloy:         -   removing equipment from the bath area, and         -   replacing said equipment with the box (70),     -   to switch to the configuration for producing annealed strip         dip-coated with a metal alloy:         -   removing the box, and         -   replacing with the equipment of the bath area.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will become apparent from the detailed description that follows, for the understanding of which reference is made to the appended drawings, in which:

FIG. 1 is a schematic view of a dual-use CAL and CGL line, in CGL mode, according to the state of the art,

FIG. 2 is a schematic view of the end of a dual-use CAL and CGL line, in CGL mode according to one embodiment of the invention,

FIG. 3 is a schematic view of the end of the dual-use CAL and CGL line of FIG. 2, but in CAL mode,

FIG. 4 is a schematic view of the end of a dual-use CAL and CGL line, in CGL mode according to a second embodiment of the invention,

FIG. 5 is a schematic view of the end of the dual-use CAL and CGL line of FIG. 4, but in CAL mode,

FIG. 6 is a schematic view of the end of a dual-use CAL and CGL line, in CGL mode according to another embodiment of the invention,

FIG. 7 is a schematic view of a cooling section, in top view, according to another embodiment of the invention,

FIG. 8 is a schematic view of the end of a dual-use CAL and CGL line, in CGL mode according to another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Since the embodiments described hereinafter are not limiting in nature, it is possible in particular to consider variants of the invention that comprise only a selection of the features that are described, provided that this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection comprises at least one preferably functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

In the remainder of the description, elements having an identical structure or similar functions will be designated by the same references.

FIG. 1 schematically shows a portion of an annealing and galvanizing line according to the state of the art. It is shown in CGL mode, the devices that allow switching to CAL mode not being shown. Likewise, for the sake of simplification, mechanical equipment located at the line inlet, such as unwinders, welder, accumulator, etc., and that placed at the line outlet, such as accumulator, shears, rewinders, etc., are neither described nor shown in the drawings. Likewise, installation equipment that is not useful for understanding the invention is neither described nor shown in the drawings, such as surface preparation equipment (stripping, degreasing, rinsing, etc.) placed upstream of the furnace, or a phosphating section placed at the exit from the furnace. The heating, maintaining and cooling sections are represented very schematically in the drawings by rectangles. They may comprise several chambers, each of which may have different heating or cooling means, for example with heating by direct flames, by radiation or by induction and cooling by blowing a cooling gas, by spraying a liquid that may or may not be oxidizing, or by using a mixture of gas and liquid. Finally, most of the equipment necessary for conveying the strip is neither described nor shown, such as deflector rollers, strip traction rollers, strip guide rollers, etc.

The line portion shown in FIG. 1 comprises, in the direction of travel of the strip:

-   -   an inlet airlock 1 for the strip B in the furnace to prevent air         from entering the furnace and to limit the leakage of the         protective gas present in the furnace (typically a mixture of         nitrogen and hydrogen),     -   a strip heating section 2, which may comprise a first direct         flame heating chamber and a second radiant tube heating chamber,     -   a section 3 for maintaining the temperature of the strip,     -   a slow cooling section 4 of the strip,     -   a rapid cooling section 5 of the strip,     -   an overaging section 6 of the strip,     -   a section 7 for final cooling of the strip,     -   a section 8 for heating the strip by induction,     -   a section 9 for deflection of the strip and for adjusting the         traction of the strip,     -   an immersion tunnel 10 equipped with a sealing system 10 a, for         example with shutters, not shown in this figure,     -   a tunnel shoe 11 placed at the outlet of the immersion tunnel         and immersed in a bath 12 of molten coating, said bath 12 of hot         coating being used to coat the strip, itself equipped with a         bottom roll 12 a allowing the path of the strip to be modified,     -   a system 13 for squeezing the strip with gas blades, independent         of whether it is equipped with a system for stabilizing the         strip,     -   a cooling tower 14 equipped with:         -   a galvannealing section 15, comprising equipment 15 a for             heating the strip by induction and a chamber 15 b for             maintaining the temperature of the strip, said section 15             being movable to be placed offline when not in use,         -   a section 16 for cooling the strip on the rising strand             comprising four cooling units 16 a, 16 b, 16 c and 16 d,         -   two rollers 17 located at the top of the cooling tower to             ensure the deflection of the strip,         -   a section 18 for cooling the strip on the descending strand             comprising three cooling units 18 a, 18 b and 18 c,         -   a set 19 of tension rollers with two rollers,         -   a section 20 for additional cooling by spraying water,             comprising a water tank 20 a, a squeezing section 20 b and a             dryer 20 c.

One embodiment of the invention is shown schematically in FIG. 2, the line being in CGL mode. In this figure, compared to FIG. 1, only the end of the line is shown. The capacity of this line is identical to that of the line shown in FIG. 1, in particular in terms of the maximum running speed of the strip and of the reference format for the strip. The overaging section 6 is similar to that of FIG. 1, that is to say, for a given strip format, it allows the same residence time of the strip at the same maintenance temperature. Conversely, the final cooling section 7 is greatly reduced compared to the state of the art, only one strip pass being retained. By “strip pass,” the present description refers to a vertical path of the strip, here from the bottom to the top.

In another embodiment of the invention, depending on the strip formats and the thermal cycles to be carried out, the final cooling section 7 may be absent, the cooling of the strip being carried out only in the cooling tower, and, if necessary, downstream thereof.

The cooling tower 14 comprises means on the rising strand for cooling the rising strand.

Each of the cooling means may be a cooling section 30, as shown in FIG. 2. The four cooling sections 30 can be sealingly connected to one another so as to obtain a sealed cooling tunnel 31.

Alternatively, the cooling means can comprise other cooling means. For example, the cooling sections 30 can be arranged on the lower part of the rising strand, the other cooling means being on the upper part.

Alternatively or in a complementary manner, the cooling sections 30 can be connected to one another in a sealed manner by means of connecting tunnels 38 (not shown) interposed between two cooling sections. The connecting tunnels interposed between two cooling sections also make up the sealed cooling tunnel 31.

A plenum 40 supplies gas to the cooling sections 30. A fan 41 is arranged on the connecting pipe between the plenum 40 and a cooling section 30 so as to adjust the cooling capacity of the cooling section separately from the other cooling sections. As a variant, another flow rate regulator, such as a valve, can be installed on this connecting pipe in addition to or as a replacement for the fan 41. By equipping several cooling sections in this way, it is possible to adjust the cooling curve of the strip along the cooling tower. A fan 43 and a heat exchanger 44 are arranged at the intake of the plenum 40, the latter being in the open air. The heat exchanger makes it possible to keep the cooling gas at the desired temperature at the inlet of the cooling sections by means of a heat transfer fluid, for example water. As we will see below, this exchanger 43 is particularly useful when the line is operating in CAL mode.

In CGL mode, the coolant that circulates in the plenum 40, the cooling sections 30 and the sealed cooling tunnel 31 is air. Since the strip is coated, there is no problem of oxidation of the strip.

A sealing airlock 13 is connected, directly or indirectly via a connecting tunnel, in a sealed manner to the last cooling section 30 in the direction of travel of the strip. Since this airlock is useful in CAL operation, it will be described below. It can be kept open in CGL mode.

In addition, in CGL mode, the equipment for the bath area is in place. This equipment in particular comprises the tank containing the coating bath 12, the bath mechanics (in particular a bottom roll 12 a), and the machine 13 for squeezing the strip at the outlet of the bath. A galvannealing section 15 comprising a heating zone 15 a followed by a holding zone 15 b is placed downstream of the squeezing machine and upstream of the cooling sections 30. This galvannealing section is removable to be taken offline when not in use.

The shoe 11 at the end of the immersion tunnel 10 plunges into the bath and provides a hydraulic seal, preventing the atmosphere of the furnace from escaping. When the bath equipment is removed to switch to CAL mode, the submerged part of the shoe is “soiled” by residues from the bath. It is thus advantageous to have a removable shoe so as to remove it when switching to CAL mode in order to be connected to the immersion tunnel.

FIG. 3 illustrates the line shown in FIG. 2 after it has been modified for operation in CAL mode. The equipment in the bath area has been removed. A box 70 provides a sealed connection and fluid continuity between the immersion tunnel 10 and the first cooling section 30 of the rising strand of the cooling tower 14, or the galvannealing section 15 if the latter is present because it is not removable. In this case, the galvannealing section must be impermeable. The sealing system 10 a of the immersion tunnel is kept open. The box 70 comprises a deflector roll 71 arranged substantially in place of the bottom roll 12 a of the bath mechanics.

The airlock 13 is kept closed in order to limit the gas leakage rate, correspondingly reducing the operating cost of the line. The sealed box 70 and the cooling sections 30 are thus maintained under a protective atmosphere, which does not oxidize the strip, as in the furnace. The intake of the fan 43 is connected to the box 70 by means of a pipe 45. Thus, the gas blown onto the strip through the cooling sections 30 is non-oxidizing gas for the strip. This protective gas is thus recirculated by being sucked in at the box 70, led to the plenum 40 via the pipe 45. The heat exchanger 44 placed at the inlet of the plenum 40 makes it possible to discharge the calories taken from the strip. The recirculated gas is thus brought back to a suitable temperature before again being projected onto the strip.

Furthermore, the installation comprises devices, not shown, making it possible to quickly purge the equipment when switching from a CAL to a CGL operating mode and vice versa. Purging makes it possible to replace the air with a non-oxidizing atmosphere, and vice versa, in particular in the immersion tunnel, the box 70, the cooling sections 30, the tunnel 31, the plenum 40 and the connecting pipes.

Description of the Main Steps for Switching the Line from CGL Mode to CAL Mode

The strip is stopped. The chamber 10 a of the immersion tunnel is closed so as to limit the leakage of the atmosphere from the furnace during line conversion operations. The shoe 11 of the immersion tunnel is removed, and the squeezing machine 13, the bath mechanics and its bottom roll 12 a and the bath 12 are removed. The galvannealing section 15 is taken offline. The strip is cut. The waterproof box 70 and the deflector roll 71 are installed in place of the bath equipment. The two ends of the strip are welded together. The sealed connections between the box 70 and the immersion tunnel 10 on the one hand, and the first cooling section 30 on the other hand, are made. The connecting pipe 45 is connected to the box 70 and to the intake of the fan 43. The airlock 13 located at the outlet of the rising strand of the strip in the cooling tower is closed and brought online. The box 70, the tunnel 31, the plenum 40 and the connecting pipes are purged with cooling gas until the oxygen content in this equipment drops to the target value. The airlock 10 a of the immersion tunnel is open. The strip is re-energized and set in motion again.

Description of the Main Steps for Switching the Line from CAL Mode to CGL Mode

The strip is stopped. The airlock 10 a of the immersion tunnel is closed. The airlock 13 located at the outlet of the rising strand of the strip in the cooling tower is open. The cooling gas used in CAL mode is purged with air. The strip is cut and each end of the strip is removed from the box 70. The connecting pipe 45 between the box 70 and the plenum 40 is disconnected. The sealed box 70 and the deflector roll 71 are moved. The shoe 11 of the immersion tunnel, the bath 12, the bath mechanics and the squeezing machine 13 are installed. The galvannealing section 15 is brought online. The two ends of the strip are welded together. The shoe 11 is immersed in the bath 12, the airlock 10 a is open, the strip is energized and then running. Note that the chronology of operations to start production is the same as that used when changing baths and bath equipment.

Another embodiment of the invention is shown schematically in FIG. 4, the line being in CGL mode. The configuration of the cooling tower 14 is similar to that of FIG. 1. In this variant embodiment, the fan 44 and the heat exchanger 43 that were placed at the inlet of the plenum 40 in the previous example are replaced by fans 41 and heat exchangers 42 placed on the connecting pipes between the plenum 40 and the cooling sections 30. Like in the previous example, the intake of the plenum 40 is in the open air in CGL mode, the valve 63 being open. A second plenum 50 is placed at the outlet of the cooling sections 30. Each cooling section is connected to the second plenum 50 by a pipe comprising an exhauster 51. A pipe 60 comprising a valve 62 connects the two plenums 40 and 50. The vent hole of the plenum 50 is in the open air in CGL mode, the valve 61 being open and the valve 62 being closed so that there is no flow in the pipe 60. The second plenum 50 collects the cooling gas after exchange with the strip. This is of great interest in CAL mode, as we will see below.

In FIG. 5, the line shown in FIG. 4 has been configured in CAL mode. The equipment of the bath area has been removed and replaced by the box 70 and its deflector roll 71. The valve 63 at the intake of the plenum 40 is closed as well as the valve 61 at the vent hole of the plenum 50. The box 70 and the tunnel 31 are maintained in a non-oxidizing atmosphere. The valve 62 on the pipe 60 is opened so that cooling gas is recirculated. FIG. 7 schematically illustrates another embodiment of the invention comprising a recirculation loop 49 per cooling section 30. In CAL mode, a non-oxidizing gas is recirculated in the circuit 49 by means of a fan 41, the two valves 46 being open and the two valves 47, 48 being closed, the exchanger 42 making it possible to discharge the calories extracted from the strip by a heat transfer fluid. In CGL mode, the recirculation circuit is closed by means of the two valves 46; the two valves 47 and 48 for venting the circuit are open. The strip B is thus cooled with non-recirculated air.

In the case where the horizontal strand does not comprise cooling sections 30, as shown in FIG. 6, a tunnel 36 provides a sealed connection between the cooling sections 30 of the descending strand and those of the rising strand.

According to another embodiment shown in FIG. 8, one or more cooling sections 30 sealingly connected to one another so as to obtain a sealed cooling tunnel 32 are placed on the horizontal connecting strand between the rising strand and the descending strand of the cooling tower. A connecting tunnel 33 connects these cooling sections 30 with those of the rising strand.

According to the embodiment of the invention shown in FIG. 8, the descending strand also comprises a set of cooling sections 30 sealingly connected to one another so as to obtain a sealed cooling tunnel 34. All of the cooling means of the descending strand of the tower can be cooling sections 30. If not all of them are, the cooling sections 30 are arranged on the upper part of the descending strand, the other units being on the lower part. In the upper part of the tower, a tunnel 35 provides a sealed connection between the cooling sections 30 of the descending strand and those of the horizontal connecting strand between the rising strand and the descending strand.

Sealingly connected end to end, the cooling sections 30 and the connecting tunnel(s) 31, 32, 33, 34, 35, 36 constitute a sealed cooling tunnel 37. This can extend:

-   -   on the rising strand only by being made up of the tunnel 31,     -   on the rising strand and the horizontal strand consisting of         tunnels 31, 32 and 33,     -   on the rising strand, the horizontal strand, and the descending         strand consisting of the tunnels 31, 32, 33, 34 and 35 or the         tunnels 31, 34 and 36.

According to another embodiment of the invention that is not shown, the cooling sections 30 are supplied by at least two plenums 40 and the cooling gas is collected by at least two plenums 50 after blowing on the strip. For example, one plenum 40 a serves the cooling sections of the rising strand and a second plenum 40 b serves the cooling sections of the descending strand, any cooling sections of the horizontal strand being connected to the first or to the second plenum. Likewise, one plenum 50 a collects the cooling gas coming from the cooling sections of the rising strand and a second plenum 50 b collects that coming from the cooling sections of the descending strand, any cooling sections of the horizontal strand being connected to the first or to the second plenum.

As a variant embodiment, the fluid used in the cooling sections 30 can be a mixture of a gas and a sprayed liquid, for example water in CGL mode and a non-oxidizing liquid for the strip in CAL mode.

As will be readily understood, the invention is not limited to the examples that have just been described, and numerous modifications can be made to these examples without departing from the scope of the invention. In addition, the various features, forms, variants, and embodiments of the invention can be grouped together in various combinations as long as they are not incompatible or mutually exclusive. 

1. Cooling tower for a continuous treatment line for metal strips having a dual purpose, which has a configuration for producing strips that are annealed and dip-coated and a configuration for producing strips that are annealed and not coated, characterized in that it is intended to operate in both line configurations and it comprises blowing means for cooling the strip selectively under a non-oxidizing atmosphere in the configuration for uncoated annealed strips and under air in the configuration for annealed and coated strips.
 2. Cooling tower according to claim 1, further comprising cooling sections connected together to form a sealed cooling tunnel.
 3. Cooling tower according to claim 2, wherein the sealed cooling tunnel is further formed by connecting tunnels interposed between two cooling sections and/or other elements.
 4. Cooling tower according to claim 2, wherein the sealed tunnel extends only over a rising strand.
 5. Cooling tower according to claim 2, wherein the sealed tunnel extends over a rising strand and a descending strand.
 6. Cooling tower according to claim 1, further comprising, in the direction of travel of the strip, in the configuration for producing uncoated annealed strips, means for sampling a non-oxidizing atmosphere present at the strip upstream of the blowing means, means for recirculating and cooling said sampled atmosphere, the blowing means being arranged to blow the sampled, cooled and recirculated atmosphere.
 7. Method for switching from one configuration to another of a cooling tower according to claim 1, characterized in that it comprises the following steps: for switching to the configuration for producing strips that are annealed and not dip-coated with a metal alloy, connecting the blowing means to a non-oxidizing atmosphere, for switching to the configuration for producing annealed and coated strips: connecting the blowing means to air.
 8. Cooling tower for a continuous treatment line for metal strips having a dual purpose, which has a configuration for producing strips that are annealed and dip-coated and a configuration for producing strips that are annealed and not coated, comprising a cooling tower according to claim
 1. 9. Line according to claim 8, comprising, successively in the direction of travel of the strip, an immersion tunnel, a bath area provided with equipment in said configuration for producing strips that are annealed and dip-coated in a metal alloy, wherein the bath area is removable and can be replaced by a box designed to provide a sealed fluid connection between the immersion tunnel and the cooling tower.
 10. Line according to claim 8, not comprising a final cooling section.
 11. Method for switching from one configuration to another of a treatment line for the continuous treatment of metal strips having a dual purpose according to claim 8, comprising the steps of the method for switching from said configuration to said other configuration of a cooling tower according to claim 7 and further comprising the following steps: to switch to the configuration for producing annealed strips not dip-coated in a metal alloy: removing equipment from the bath area, and replacing said equipment with the box, to switch to the configuration for producing annealed strip dip-coated with a metal alloy: removing the box, and replacing with the equipment of the bath area. 